In order to use superconducting technologies to measure electrical waveforms produced by room temperature devices, or indeed to interface any low temperature electronic device to a room temperature electronic device, the interface mechanism must satisfy certain electrical, mechanical, and temperature constraints. Co-pending patent application No. 796,842, filed on Nov. 11, 1985 now U.S. Pat. No. 4,715,189, which is related to the present invention, discusses the aforementioned constraints and attempts of the prior art to satisfy them. The invention described and claimed in the above co-pending patent application obviates the problems of the prior art mechanisms.
Existing apparatus which actually deliver cold fluids to a sample to be cooled also have numerous drawbacks that must be overcome. One example of existing product used in the field of optics to cool devices is known by the trademark Heli-Tran and made by APD Cryogenics, Inc., Allentown, PA.
The Heli-Tran comprises a mounting head enclosed in an evacuated space for holding a sample to be cooled, and a multi-channel flexible transfer tube for connecting the mounting head to a dewar of liquid helium. The descriptive literature appears to show that the transfer tube comprises a forward helium flow capillary (from the dewar to the mounting head), a shield tube surrounding the forward helium flow capillary, and a separate return flow capillary for the spent fluid. When the dewar is pressurized, liquid helium flows through both the forward helium flow capillary and the shield tube into the mounting head. The helium in the capillary strikes the inside surface of a metal block closing off the end of the transfer tube, then enters a passage coaxially surrounding all the transfer tube elements, travels a short distance in the return direction, and exits through a helium exhaust port. The helium in the shield tube turns back at the metal block, enters the return flow capillary, and exits from a shield flow return port near the dewar. The sample holder is attached to the outside of the metal block so that it can conduct heat from the sample to be cooled to the metal block, which in turn is cooled by the helium in the forward flow capillary.
The primary drawbacks with the Heli-Tran system are that the mounting head is entirely enclosed in a vacuum shroud, rendering sample demounting difficult and cumbersome and that the descriptive literature suggests total immersion of the samples, e.g., a superconducting electronic circuit, contributing to inefficient liquid helium consumption.